The present invention relates generally to an improved method of purifying crude pyrethrum extract and more specifically to a method of purifying crude pyrethrum extract through the use of acetonitrile (methyl cyanide) as the extracting agent.
Pyrethrum is one of the oldest and most widely used insecticides primarily because of its effectiveness against a wide variety of insects and because of its relatively low degree of toxicity to humans and animals. Further, unlike many other insecticides, pyrethrum does not appear to induce resistance in insects which are exposed to a sublethal dose of the same.
Crude pyrethrum extract is normally manufactured by solvent extraction or treatment of dry pyrethrum flowers to form a crude pyrethrum extract. There are essentially two methods currently in use to accomplish such extraction. One is percolation with petroleum ether in a batch system. The other is a continuous flow system in which a countercurrent extraction system is utilized. In some areas, this crude extract is centrifuged to remove some of the heavier solids whereas, in other areas, a process is used to standardize the crude extract to 25% by the addition of a petroleum solvent such as deodorized kerosene. This crude extract as shipped is a dark viscous oleoresin and usually contains from 25% to 40% pyrethrins. Such crude extract also includes relatively large amounts of impurities such as colored extractives, resins, fatty acids and the like, which, among other things, render the eventual refined extract undesirable from a color standpoint if not removed and cause such refined extract to lack stability. To a certain extent, these impurities precipitate out when the extract is diluted with deodorized kerosene to usable concentrations; however, a large percentage of the impurities remain in the crude extract after such dilution.
The subject matter of the present invention relates to an improved process to further refine this crude pyrethrum extract to a concentrated refined pyrethrum extract which can be readily used and is desirable to use in the preparation of, among other things, insecticides. It is highly desirable to obtain such a refined extract with little or no unsaturated fatty acids since such fatty acids tend to react with metals such as iron, cadmium, copper, zinc and lead to form insoluble precipitates. The fatty acids also tend to oxidize and form peroxides which in turn degrade the pyrethrins in storage. It is also desirable to have a more efficient refining process which provides an improved quality of refined pyrethrum. Finally, it is desirable to provide a refined extract with improved color quality to prevent staining of fabrics and the like when the refined extract is used as an ingredient in insecticides.
The present invention provides for the purification or refining of crude pyrethrum extract through the use of acetonitrile as the extracting agent and includes the following steps: Extracting the crude pyrethrum which constitutes approximately 25% to 40% pyrethrins with acetonitrile (methyl cyanide); allowing the mixture to separate and drawing off the solvent extract layer at a temperature sufficiently low to satisfactorily remove the waxes and various other precipitates remaining in the solvent extract and formed as a result of the reduced temperature; removing the resulting solid particles by filtration and removing the acetonitrile by distillation; diluting the recovered pyrethrum extract with mineral spirits such as a light isoparaffinic solvent and adding decolorizing activated carbon to this solution to remove unwanted color bodies; filtering the solid particles from this resulting solution; and distilling the solution to remove the mineral spirits. The resulting product is a refined pyrethrum extract useable in, among other things, the manufacture of insecticides.
Accordingly, it is an object of the present invention to provide an improved method of refining crude pyrethrum which produces a higher quality refined pyrethrum extract.
Another object of the present invention is to provide a method of refining crude pyrethrum extract through the use of acetonitrile (methyl cyanide).
A further object of the present invention is to provide a method for refining crude pyrethrum extract to produce a refined extract having a color quality which is improved over prior methods.
Another object of the present invention is to provide a method for refining crude pyrethrum extract to produce a refined extract having improved stability and an improved yield over prior methods.
Another object of the present invention is to provide a method for refining crude pyrethrum extract in which a refined extract is produced which is free of impurities which might precipitate out upon standing for an extended time.
These and other objects of the present invention will become apparent with reference to the description below of the preferred method and to the appended claims.